1. Field of the Invention
The present invention relates to an original reader for use in an image-forming apparatus and more particularly to such original reader which is able to read even those originals having high regular reflectance.
2. Description of the Prior Art
At present there are many types of apparatus which include an original reader for reading an original illuminated by illumination means. A typical example of such apparatus is an image-forming apparatus such as copying machine or facsimile equipment. However, the prior art reader generally used in such type of apparatus has a limitation that the reader can read the original only when the surface of the original is low in regular reflectance. It can not read those originals having high regular reflectance.
For example, U.S. Pat. Nos. 3,994,582 and 4,124,296 have disclosed image-forming apparatus in which an original is placed directly on a platen glass and then the original is covered with an original pressing plate for reading the original. In this case, if the original is high in regular reflectance, a large portion of the illumination light incident on the original will be regular-reflected at a reflection angle corresponding to the incidence angle. Therefore, image sensor means in the apparatus does not receive sufficient light from the original. The result is under-exposure. When the image-forming apparatus is an electrophotographic copying machine, the under-exposure renders the obtained copy totally black. For a facsimile equipment, it is impossible to obtain any data concerning the image. This problem will be described in further detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic sectional view of an original reader according to the prior art used in an electrophotographic copying machine.
An original 1 is placed on a platen glass 2 and covered with an original pressing plate 13 having a white sheet 14. The original 1 is illuminated and scanned by illumination means (comprising an original illumination lamp 3 and a reflector 5). Said illumination means runs leftward and rightward under the platen glass while obliquely illuminating the original 1 from underneath.
If the original 1 is an ordinary paper sheet of high diffuse reflection factor, then the illumination light 8 will be diffuse-reflected upon the surface of the original. Therefore, in this case, the first mirror 6.sub.1 can receive a sufficient quantity of reflected light to form an image of the original. The first mirror 6.sub.1 reflects the light to the second mirror 6.sub.2 through which the reflected light enters a lens 6.sub.4. According to the principles of conventional electrophotographic processes, the reflected light is read in a photosensitive drum 6.sub.3 through image sensor means including the lens 6.sub.4.
However, if the original 1 has a high regular reflectance, a large portion of the illumination light 8 is regular-reflected upon the original surface as indicated by arrow 9. The first mirror 6.sub.1 can receive almost no reflected light from the original 1. Because of the shortage of exposure, there obtained only blackened image.
FIG. 2 shows the prior art original reader in a facsimile equipment. Like reference characters to FIG. 1 represent the same or corresponding elements which need not be further described.
Also, in this case, if the original 1 is of high regular reflectance, the reflected light 7 can scarcely reach image sensor means such as CCD through a bar lens 6.sub.5. Therefore, the facsimile equipment can not pick up images because of the lack of the effective illumination from the original.